I have also tried to solve this in Ubuntu 12.04 running mate desktop environment.
My solution looks like this:
google-chrome --user-data-dir=/home/loafer/.userscripts/chrome-bg-profile --kiosk http://localhost/bg &
wmctrl -r "localhost/bg/ - Google Chrome" -b add,below
I have created a script file with the content above to run at startup. The first command runs google chrome in kiosk mode (borderless window without controll elements in fullscreen) with a seperate user data directory. You have to define a data directory or else chrome won't let you start non-kiosk instances afterwards. I pointed the kiosk instance to my local server, let the script sleep for 2 seconds (the time it takes for chrome to start) and afterwards I force chrome to be always below all other windows with wmctrl. Change
localhost/bg/ - Google Chrome to whatever window title your kiosk window has. You can get wmctrl from the official ubuntu repository with
sudo apt-get install wmctrl.
I hope this works for you.